Generally, in case of existing laparotomy surgery for the treatment of patients, since an incision site is large, and an amount of blood loss during the surgery is large, recovery of a patient is slow. In addition, a large scar remains after the surgery to negatively affect patient's lives in the past.
To overcome the above-described disadvantages of the laparotomy surgery, novel surgical techniques such as minimal invasive surgery (MIS) using a laparoscopic surgical instrument are being developed in recent years.
The MIS may be a surgical technique in which a thin and long surgical instrument that is specifically designed to minimize an incision site required for the surgery is used to incise only a minimal part in the body surface of the patient.
Since the incision site required for the surgery is small, and the amount of blood loss during the surgery is small in the MIS compared to that of the laparotomy surgery, the recovery of the patent is fast, an external visible scar is small. As a result, the number of MIS is being remarkably increasing in recent years.
A disc existing between vertebrae functions as a joint and plays very important roles for minimizing an impact applied to the vertebrae while vertebral pulp accommodated inside the disc changes in position and shape according to the movement of the vertebrae.
The vertebral pulp is mostly moisture (water). When we get older, an amount of moisture gradually decreases, and thus, a buffer function of a disc is lost.
As a result, when an excessive pressure is applied to the fibers, backache may occur. Here, if the excessive pressure is continuously applied, the fibers may be seriously stretched or ruptured to push nerve roots placed at a rear side thereof, thereby causing pains of pelvis, legs, and the like.
Thereafter, a distance between the vertebrae gradually decreases, or the vertebrae are collapsed to cause various kinds of side effects such as vertebral deformation.
There is a method, in which an intervertebral fusion device, so-called, a cage is inserted between two adjacent vertebrae after a disc between the damaged vertebrae is removed, as a method for treating diseases involved due to the disc.
That is, the cage recovers the distance between the vertebrae to its original distance between the two adjacent vertebrae, which corresponds to an original height of the disc, thereby recovering the vertebral function.
The surgical method in which the cage is inserted between the vertebrae includes an anterior lumbar interbody fusion (ALIF) method in which a cage is inserted from a front side of a vertebra after an abdominal operation, a lateral lumber interbody fusion (LLIF) method in which a cage is inserted through a side portion, a transforaminal lumbar interbody fusion (TLIF) method in which a cage is inserted in a diagonal direction at a point that is spaced a distance of 30 mm to 40 mm laterally from a center of a back, a posterior lumbar interbody fusion (PLIF) method in which a cage is inserted from a back, and the like.
For example, there is an “intervertebral fusion device” (hereinafter, referred to as a ‘prior art’) disclosed in Korean Patent Registration No. 10-1371418.
The prior art has a structure including: a vertical rear part; top and bottom surfaces respectively integrated with upper and lower portions of the rear part to face each other and extending to be gradually widened forward from the rear part; a top surface front part having a curvature that is convexly curved from an extension end of the top surface to the bottom surface; a bottom surface front part having a curvature that is convexly curved from an extension end of the bottom surface to the top surface; and a through-hole for synostosis of the top and bottom surfaces.
However, most cages according to the prior art are vulnerable to torsion stress applied between the top and bottom surfaces and the rear part when a subject person perform motion such as twisting of his/her waist after the surgery. Also, when the cages are used for a long time, the cages are faced with a fatal problem such as breakage of the connection portion.
Also, in the most cages according to the prior art, when each of the cages is inserted between a vertebra and an adjacent vertebra during the surgery, since a front end of the cage does not have a sharp shape, tissues such as blood vessels or nerves may be damaged while the cage is inserted through an opening of the subject person.
Thus, the damage due to the torsion stress may act as a factor that causes pain of the patient again. As a result, it is highly likely that the patient has to re-operate and thus suffers pain again.